diff --git a/test/plugin_helper/test_child_process.rb b/test/plugin_helper/test_child_process.rb
index 498277d06b..186ef01e46 100644
--- a/test/plugin_helper/test_child_process.rb
+++ b/test/plugin_helper/test_child_process.rb
@@ -286,9 +286,11 @@ def configure(conf)
       assert_equal [], @d.log.out.logs
 
       @d.stop # nothing occurs
-      sleep TEST_WAIT_INTERVAL_FOR_LOOP
-      lines1 = ary.size
-      assert{ lines1 > 1 }
+      lines1 = nil
+      waiting(TEST_WAIT_INTERVAL_FOR_LOOP * 3) do
+        lines1 = ary.size
+        lines1 > 1
+      end
 
       pid = @d._child_process_processes.keys.first
       # default value 10 is too long for test